RPR 10981 is an orally active antagonist of the platelet glycoprotein (GP) IIb/IIIa complex, also known as the fibrinogen receptor. This receptor is the final common mediator in the cross linkage of activated platelets to form an aggregate. GP IIb/IIIa antagonists inhibit platelet aggregation regardless of the agonist used to induce aggregation. Recent large scale trials have demonstrated that the administration of GP IIb/IIIa antagonists induces a significant reduction in adverse ischemic clinical outcomes following coronary angioplasty. The present study will evaluate the safety and pharmacodynamic response of 3 doses (75,100, 125 mg) of RPR 109891 plus aspirin compared to placebo plus aspirin in patients with recent (<14 days) acute coronary artery syndromes. RPR 109891 will be given bid for 60 days. Platelet aggregation, bleeding time and plasma levels RPR 109891 and its active metabolite will be assessed on day 1, 5 and 30. A total of 320 patients will be enrolled in 25 centers.